One general type of sound suppressor or silencer now available includes an assembly of spaced baffles located in an outer casing or housing. These baffles may be perpendicular to the bore, conical (usually rearwardslanting), or helical. The spacing between the baffles provides discrete expansion chambers.
A somewhat different, but structurally similar approach includes packing the outer casing with washer-like members cut from, for example, woven wire screen mesh or compressed knitted wire mesh.
The above types of silencers have a central bore for passage of the projectile. This bore is larger than the projectile to preclude contact between the silencer and the projectile which could result in loss of accuracy and damage to the silencer.
Extensive research has been conducted over the years with baffle-type silencers, the better examples of which perform well accoustically However, baffle-type silencers are difficult and expensive to manufacture, which has significantly limited their utilization. This difficulty is due to the conflicting requirement of minimum clearance for the projectile to yield maximum attenuation, and the multiplicative tolerances of the components which must be maintained to ensure alignment along these lines (see pages 23 and 54 of AMF Final Report Phase III, Paladin Press). These types of suppressors suffer from the disadvantage of being relatively heavy. Such suppressors are unlikely to be interchangeable between guns of the same model and can be easily misaligned by rough handling in the field. For the most part, these suppressors have to be custom made and fitted for any particular weapon.
The wire screen washer packed silencer performs well, both accoustically and as a muzzle flash reducer, when initially installed. The good performance is believed to be due to the rapid heat exchange between the propellant gases and the large surface area of conductive metal. Such silencers are generally more efficient on a volume basis and for a given projectile clearance than baffle silencers. Accordingly, those types of silencers can be smaller than baffle silencers while achieving similar performance.
However, gradual fraying of the cut woven mesh packing requires periodic maintenance. In addition, such can be easily misaligned by rough handling in the field. A few isolated suggestions have appeared in the literature that a thin walled central tube can be used to support packing material. Specifically, it has been suggested to wrap the thin walled tube with packing such as screen, steel wool, fiberglass, metal shavings, and turnings.